In recent years, applications that need pattern matching such as character recognition and image recognition have attracted much attention. If implemented on LSIs (Large Scale Integrated Circuits), the pattern matching may be applicable to highly functional applications such as artificial intelligence and mobile equipment in the future, which particularly gathers considerable attention.
The pattern matching includes “exact match search processing” to search a plurality of reference data pieces stored in a database for an exact match with the search data and “most similar match search processing” to search for the most similar pattern to the search data.
The former is called CAM “Contents Addressable Memory” and used e.g. for exact-much search with an IP address table in network routers or for implementing caches and virtual memory in a processor. In order to have a computer carry out flexible search/comparison like what is carried out by human brain, implementation of the latter “most similar match search processing” is imperative. A memory capable of implementing such flexible comparison is specially called “associative memory.”
Proposed means for implementing an associative memory includes (1) a digital way of implementation (Non-Patent Document 1), (2) an analog way of implementation, and (3) a mixed digital-analog way of implementation (Non-Patent Document 2).